51 research outputs found
Shallow water marine sediment bacterial community shifts along a natural CO2 gradient in the Mediterranean Sea off Vulcano, Italy.
The effects of increasing atmospheric CO(2) on ocean ecosystems are a major environmental concern, as rapid shoaling of the carbonate saturation horizon is exposing vast areas of marine sediments to corrosive waters worldwide. Natural CO(2) gradients off Vulcano, Italy, have revealed profound ecosystem changes along rocky shore habitats as carbonate saturation levels decrease, but no investigations have yet been made of the sedimentary habitat. Here, we sampled the upper 2 cm of volcanic sand in three zones, ambient (median pCO(2) 419 μatm, minimum Ω(arag) 3.77), moderately CO(2)-enriched (median pCO(2) 592 μatm, minimum Ω(arag) 2.96), and highly CO(2)-enriched (median pCO(2) 1611 μatm, minimum Ω(arag) 0.35). We tested the hypothesis that increasing levels of seawater pCO(2) would cause significant shifts in sediment bacterial community composition, as shown recently in epilithic biofilms at the study site. In this study, 454 pyrosequencing of the V1 to V3 region of the 16S rRNA gene revealed a shift in community composition with increasing pCO(2). The relative abundances of most of the dominant genera were unaffected by the pCO(2) gradient, although there were significant differences for some 5 % of the genera present (viz. Georgenia, Lutibacter, Photobacterium, Acinetobacter, and Paenibacillus), and Shannon Diversity was greatest in sediments subject to long-term acidification (>100 years). Overall, this supports the view that globally increased ocean pCO(2) will be associated with changes in sediment bacterial community composition but that most of these organisms are resilient. However, further work is required to assess whether these results apply to other types of coastal sediments and whether the changes in relative abundance of bacterial taxa that we observed can significantly alter the biogeochemical functions of marine sediments
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Culex pipiens development is greatly influenced by native bacteria and exogenous yeast
Culex pipiens is the most cosmopolitan mosquito of the Pipiens Assemblage. By studying the nature of interactions between this species and microorganisms common to its breeding environment we can unravel important pitfalls encountered during development. We tested the survival rate of larval stages, pupae and adults of a Cx. pipiens colony exposed to a variety of microorganisms in laboratory conditions and assessed the transmission to offspring (F1) by those organisms that secured development up to adulthood. Three complementary experiments were designed to: 1) explore the nutritional value of yeasts and other microorganisms during Cx. pipiens development; 2) elucidate the transstadial transmission of yeast to the host offspring; and 3) to examine the relevance of all these microorganisms in female choice for oviposition-substratum. The yeast Saccharomyces cerevisiae proved to be the most nutritional diet, but despite showing the highest survival rates, vertical transmission to F1 was never confirmed. In addition, during the oviposition trials, none of the gravid females was attracted to the yeast substratum. Notably, the two native bacterial strains, Klebsiella sp. and Aeromonas sp., were the preferred oviposition media, the same two bacteria that managed to feed neonates until molting into 2nd instar larvae. Our results not only suggest that Klebsiella sp. or Aeromonas sp. serve as attractants for oviposition habitat selection, but also nurture the most fragile instar, L1, to assure molting into a more resilient stage, L2, while yeast proves to be the most supportive diet for completing development. These experiments unearthed survival traits that might be considered in the future development of strategies of Cx. pipiens control. These studies can be extended to other members of the Pipiens Assemblag
Spatial and Temporal Dynamics of Hepatitis B Virus D Genotype in Europe and the Mediterranean Basin
Hepatitis B virus genotype D can be found in many parts of the world and is the most prevalent strain in south-eastern Europe, the Mediterranean Basin, the Middle East, and the Indian sub-continent. The epidemiological history of the D genotype and its subgenotypes is still obscure because of the scarcity of appropriate studies. We retrieved from public databases a total of 312 gene P sequences of HBV genotype D isolated in various countries throughout the world, and reconstructed the spatio-temporal evolutionary dynamics of the HBV-D epidemic using a Bayesian framework
Challenging the Wigglesworthia, Sodalis, Wolbachia symbiosis dogma in tsetse flies : Spiroplasma is present in both laboratory and natural populations
Profiling of wild and laboratory tsetse populations using 16S rRNA gene amplicon sequencing allowed us to examine whether the “Wigglesworthia-Sodalis-Wolbachia dogma” operates across species and populations. The most abundant taxa, in wild and laboratory populations, were Wigglesworthia (the primary endosymbiont), Sodalis and Wolbachia as previously characterized. The species richness of the microbiota was greater in wild than laboratory populations. Spiroplasma was identified as a new symbiont exclusively in Glossina fuscipes fuscipes and G. tachinoides, members of the palpalis sub-group, and the infection prevalence in several laboratory and natural populations was surveyed. Multi locus sequencing typing (MLST) analysis identified two strains of tsetse-associated Spiroplasma, present in G. f. fuscipes and G. tachinoides. Spiroplasma density in G. f. fuscipes larva guts was significantly higher than in guts from teneral and 15-day old male and female adults. In gonads of teneral and 15-day old insects, Spiroplasma density was higher in testes than ovaries, and was significantly higher density in live versus prematurely deceased females indicating a potentially mutualistic association. Higher Spiroplasma density in testes than in ovaries was also detected by fluorescent in situ hybridization in G. f. fuscipe
Local environmental conditions shape generalist but not specialist components of microbial metacommunities in the Baltic Sea
Marine microbes exhibit biogeographical patterns linked with fluxes of matter and
energy. Yet, knowledge of the mechanisms shaping bacterioplankton community
assembly across temporal scales remains poor. We examined bacterioplankton 16S
rRNA gene fragments obtained from Baltic Sea transects to determine phylogenetic
relatedness and assembly processes coupled with niche breadth. Communities
were phylogenetically more related over time than expected by chance, albeit with
considerable temporal variation. Hence, habitat filtering, i.e., local environmental
conditions, rather than competition structured bacterioplankton communities in summer
but not in spring or autumn. Species sorting (SS) was the dominant assembly
process, but temporal and taxonomical variation in mechanisms was observed. For May
communities, Cyanobacteria, Actinobacteria, Alpha- and Betaproteobacteria exhibited
SS while Bacteroidetes and Verrucomicrobia were assembled by SS and mass effect.
Concomitantly, Gammaproteobacteria were assembled by the neutral model and patch
dynamics. Temporal variation in habitat filtering and dispersal highlights the impact of
seasonally driven reorganization of microbial communities. Typically abundant Baltic
Sea populations such as the NS3a marine group (Bacteroidetes) and the SAR86
and SAR11 clade had the highest niche breadth. The verrucomicrobial Spartobacteria
population also exhibited high niche breadth. Surprisingly, variation in bacterioplankton
community composition was regulated by environmental factors for generalist taxa
but not specialists. Our results suggest that generalists such as NS3a, SAR86, and
SAR11 are reorganized to a greater extent by changes in the environment compared to
specialists and contribute more strongly to determining overall biogeographical patterns
of marine bacterial communities
Unscrambling cyanobacteria community dynamics related to environmental factors
Future climate scenarios in the Baltic Sea project an increase of cyanobacterial
bloom frequency and duration, attributed to eutrophication and climate change. Some
cyanobacteria can be toxic and their impact on ecosystem services is relevant for
a sustainable sea. Yet, there is limited understanding of the mechanisms regulating
cyanobacterial diversity and biogeography. Here we unravel successional patterns
and changes in cyanobacterial community structure using a 2-year monthly timeseries
during the productive season in a 100 km coastal-offshore transect using
microscopy and high-throughput sequencing of 16S rRNA gene fragments. A total of
565 cyanobacterial OTUs were found, of which 231 where filamentous/colonial and
334 picocyanobacterial. Spatial differences in community structure between coastal and
offshore waters were minor. An \u201cepidemic population structure\u201d (dominance of a single
cluster) was found for Aphanizomenon/Dolichospermum within the filamentous/colonial
cyanobacterial community. In summer, this cluster simultaneously occurred with
opportunistic clusters/OTUs, e.g., Nodularia spumigena and Pseudanabaena.
Picocyanobacteria, Synechococcus/Cyanobium, formed a consistent but highly diverse
group. Overall, the potential drivers structuring summer cyanobacterial communities
were temperature and salinity. However, the different responses to environmental
factors among and within genera suggest high niche specificity for individual OTUs.
The recruitment and occurrence of potentially toxic filamentous/colonial clusters
was likely related to disturbance such as mixing events and short-term shifts in
salinity, and not solely dependent on increasing temperature and nitrogen-limiting
conditions. Nutrients did not explain further the changes in cyanobacterial community
composition. Novel occurrence patterns were identified as a strong seasonal succession
revealing a tight coupling between the emergence of opportunistic picocyanobacteria
and the bloom of filamentous/colonial clusters. These findings highlight that
if environmental conditions can partially explain the presence of opportunistic
picocyanobacteria, microbial and trophic interactions with filamentous/colonial
cyanobacteria should also be considered as potential shaping factors for singlecelled
communities. Regional climate change scenarios in the Baltic Sea predict
environmental shifts leading to higher temperature and lower salinity; conditions identified here as favorable for opportunistic filamentous/colonial cyanobacteria. Altogether,the diversity and complexity of cyanobacterial communities reported here is far greater than previously known, emphasizing the importance of microbial interactions between filamentous and picocyanobacteria in the context of environmental disturbance
Metapopulation theory identifies biogeographical patterns among core and satellite marine bacteria scaling from tens to thousands of kilometers
Metapopulation theory developed in terrestrial ecology
provides applicable frameworks for interpreting
the role of local and regional processes in shaping
species distribution patterns. Yet, empirical testing of
metapopulation models on microbial communities is
essentially lacking. We determined regional bacterioplankton
dynamics from monthly transect sampling
in the Baltic Sea Proper using 16S rRNA gene
sequencing. A strong positive trend was found
between local relative abundance and occupancy of
populations. Notably, the occupancy-frequency distributions
were significantly bimodal with a satellite mode of rare endemic populations and a core mode
of abundant cosmopolitan populations (e.g. Synechococcus,
SAR11 and SAR86 clade members).
Temporal changes in population distributions supported
several theoretical frameworks. Still,
bimodality was found among bacterioplankton communities
across the entire Baltic Sea, and was also
frequent in globally distributed datasets. Datasets
spanning waters with widely different physicochemical
characteristics or environmental gradients
typically lacked significant bimodal patterns. When
such datasets were divided into subsets with coherent
environmental conditions, bimodal patterns
emerged, highlighting the importance of positive
feedbacks between local abundance and occupancy
within specific biomes. Thus, metapopulation theory
applied to microbial biogeography can provide novel
insights into the mechanisms governing shifts in biodiversity
resulting from natural or anthropogenically
induced changes in the environmen
Consequences of increased terrestrial dissolved organic matter and temperature on bacterioplankton community composition during a Baltic Sea mesocosm experiment
Predicted increases in runoff of terrestrial dissolved organic matter (DOM) and sea surface temperatures implicate substantial changes in energy fluxes of coastal marine ecosystems. Despite marine bacteria being critical drivers of marine carbon cycling, knowledge of compositional responses within bacterioplankton communities to such disturbances is strongly limited. Using 16S rRNA gene pyrosequencing, we examined bacterioplankton population dynamics in Baltic Sea mesocosms with treatments combining terrestrial DOM enrichment and increased temperature. Among the 200 most abundant taxa, 62 % either increased or decreased in relative abundance under changed environmental conditions. For example, SAR11 and SAR86 populations proliferated in combined increased terrestrial DOM/temperature mesocosms, while the hgcI and CL500-29 clades (Actinobacteria) decreased in the same mesocosms. Bacteroidetes increased in both control mesocosms and in the combined increased terrestrial DOM/temperature mesocosms. These results indicate considerable and differential responses among distinct bacterial populations to combined climate change effects, emphasizing the potential of such effects to induce shifts in ecosystem function and carbon cycling in the future Baltic Sea.Supplement: 3 Special Issue: SI</p
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